Such control units generally comprise control elements for controlling functions of the domestic appliance. In the case of cooktops, it is possible to provide a control element that operates the respective hot plate of the cooktop, to activate or deactivate the hot plate, and to set the power.
In the case of cooktops, the control unit can be provided within, or on the edge of, the so-called stovetop behind a cover in the form of a glass-ceramic plate. Capacitive sensor elements are generally used as control elements, the capacitance of which changes depending on actuation or operation. This change in capacitance can be processed by an associated control unit and converted into appropriate control commands.
Since such capacitive control elements generally do not provide a tactile response when being actuated, and therefore luminous means, such as LEDs, are associated with the control elements or sensor elements. Their optical state can correspond to the actuating state or can visually indicate activation or deactivation or power setting effected by the actuation.
Such a control unit with illuminated or background-illuminated, capacitive control elements or sensor elements is disclosed in DE 103 26 684 A1. Provision is made for the control unit to be installed behind a cover in the form of a glass-ceramic plate of the domestic appliance and to have fitted a transparent, capacitive sensor element in the form of a conductive foil, which in the assembled state of the control unit is positioned on the rear face of the cover, that is to say, on the side facing away from the user. A luminous means is associated with the sensor element, for example in the form of an LED, with the light emitted laterally or parallel to the cover by the LED being deflected in the direction of the cover and scattered by an light guide. As seen from the cover, the light guide is arranged flush behind the sensor element. Since the sensor element is transparent, it can thus be backlit or have background lighting. The LED and the light guide are arranged on a side of a circuit board facing the cover. The sensor element contacts the circuit board via associated contact means or plug connectors, with the sensor signal at the sensor element being fed to a control unit for evaluation, through tracks of the circuit board.
If such a control unit is intended to be arranged in an edge area of the glass-ceramic plate or outside of the glass-ceramic plate, an overall physical height of the control element, which results from the sum of the thickness of the circuit board, the height or the thickness of the light guide and the thickness of the sensor element, must be smaller than 4 mm, for example. However, this is difficult to implement using the control unit shown in DE 103 26 684 A1, since the height or thickness of the light guide cannot be reduced arbitrarily due to the desired imaging characteristics.
Furthermore, the control unit shown requires a special interface or a special plug connector between the sensor element and circuit board.